Current control circuit



June 1967 R. E. PECZHACZEK CURRENT CONTROL CIRCUIT Filed Jan. 28,

INVENTOR. R0851? T E. P H 5 ATTORNEY United States Patent 3,327,127CURRENT CONTROL CIRCUIT Robert E. Pechacek, Berkeley, Calif., assignorto the United States of America as represented by the United StatesAtomic Energy Commission Filed Jan. 28, 1964. Ser. No. 340,838 4 Claims.(Cl. 307-60) The present invention relates in general to current controlcircuits. More particularly, this invention relates to a, currentcontrol circuit providing both current limitingregulating andnon-limiting modes of operation.

Current control circuits are generally used as protective devices toprevent undesirable load current changes. One of the primary uses ofsuch current control circuits is to protect a source of power and itsload impedance from load current changes due to load impedancevariations. Conventional current control circuits are classified aseither non-linear or degenerative. In both cases, current controlcircuits make use of an element serially connected to the load impedanceto effect either a high im- .pedance to the load or an impedancefluctuation that varies directly as the current fluctuation. Such aseries connected element will consume power under all modes of operationwith the proportion of power consumed from the load current sourcedepending upon the internal impedance of the current control circuit ascompared to the impedance of the load. Hence, under conditions whereload current'vari-ations are the result of load impedance variations thegreater the reduction of load impedance, the-more power is-consumed bythe control circuit.

Additionally, it is often desirable to provide a current control circuitwhich allows the load current to vary over a preselected range whilepreventing the load current from exceeding such range. For example, inthe field of quantitative analysis of ions, electrophoresis is a methodutilized to separate the various ions of a solution. Generally, thistechnique requires a current limiting and regulating circuit which willprotect both a strip of paper upon which the ion separation takes placeand the power supply used to establish a potential difference betweenthe ends of the stripof paper from current overload. In the applicationof the electrophoresis technique, it is of considerable importance toestablish a constant potential difference between the ends of the stripof paper. Hence, it is desirable to provide a current control circuitwhich allows load current fluctuations only over a preselected range andwhose internal impedance in the non-limiting mode is low enough so thatthe regulation of the voltage across the strip of paper is notimpairedas the impedance of the strip of paper varies.

- The present invention is a non-linear current control circuit designedto limit delivered to a load impedance. The invention comprises a diodeserially connected with a power supply and a load impedance in a mannerto normally oppose current flow from the power supply generator, whoseoutput is variable, is electrically connected in parallel With the diodein a manner to provide a predetermined forward bias current to thediode. When the load current is less than the forward bias current thediode is in the on state and hence, the current control circuit isoperating in the non-limiting -mode. When the load current is equal toor greater than the forward bias current, the diode is in the off stateand the only possible path for the 'load current is through the constantcurrent generator. In this mode of operation, the current controlcircuit is functioning in the limiting-regulating mode.

Accordingly, the present invention provides two distinct advantages overexisting current control circuits. First, the dual operating mode of thepresent current conand regulate the current being.

to the-load. A constant current.

3,327,127 Patented June 20, 1967 trol circuit allows a variation in theload current over a preselected range which is unaffected by the currentcon trol circuit. Second, since the impedance of the diode in the onstate is negligible in comparison to the load impedance, the diode Willconsume only a negligible amount of power during the non-limitingoperating mode. Furthermore, as a result of this negligible impedance ofthe diode in the non-limiting operating mode, the regulation of thevoltage across the load impedance is not affected by variations in loadcurrent.

It is therefore an object of this invention IIO provide a currentcontrol circuit having non-limiting and limitingregulating modes ofoperation.

More particularly, it is an object of this invention to provide acurrent control circuit which will prevent the load current fromexceeding a preset level which level can be varied over a considerablerange.

It is a further object of this invention to provide such a currentcontrol circuit which will allow the load current to vary in the rangebelow the preset current limit level.

It is another object of this invention to provide a current controlcircuit in which during non-limiting operating conditions, the impedanceof the current control circuit stability.

The manner of achieving these and other objects and advantages willbecome more apparent from the following detailed description taken inconnection with the accompanying drawings in which;

FIGURE 1 is an equivalent circuit diagram embodying the principles setforth by the present invention;

FIGURE 2 is an equivalent circuit diagram illustrating the non-limitingmode of operation of the current control circuit;

FIGURE 3 is an equivalent circuit diagram illustrating thelimiting-regulating mode of operation of the current control circuit;

FIGURE 4 illustrates a preferred circuit embodiment of the presentinvention.

- With reference to FIGURE 1, a non-linear current con trol circuit 11is electrically connected in series relationship with a power supply 12and a load impedance 13. Control circuit 11 comprises a diode 14electrically connected in series relationship with supply 12 and loadimpedance 13. Diode 14 is poled, i.e., current flow oriented, to opposethe fiow of load current 16 form supply 12 to the load impedance 13. Aconstant current generator 17 is electrically connected in parallel withdiode 14 and a current generator 17 is arranged to provide a forwardbias current 18 to the diode 14.

depicted by the closed position of a switch 19. Under these conditionsthe current control circuit 11 is functioning in the non-limiting modeof operation. In this mode of operation the impedance of the currentcontrol circuit 11 is that of the forward biased diode 14 which isnegligible.

As a result of the essentially zero impedance of the current controlcircuit 11 during the non-limiting mode of operation, the potentialdifference existing between terminals 21 and 22 of supply 12 istransferred directly .to load impedance 13. Thus, in the non-limitingmode 3 the potential of supply 12 is established at load 13 regardlessof load current variations resulting from load impedance fluctuations.

When the load impedance or source variations cause load current 16 tobecome at least equal to the forward bias current 18 diode 14 is biasedto be off state. Referring to FIGURE 3 the off state of diode 14 isdepicted by the open position of switch 19. Under these conditions thecontrol circuit 11 is functioning in the current limiting-regulatingmode of operation.

When in the off state diode 14 appears as an open circuit to supply 12and current generator 17. This effectuates an open circuit path whichprevents current from flowing therethrough. Consequently, the currentpath to load impedance 13 is now from positive terminal 21 of supply 12through the path including current generator 17 through load impedance13 and back to the negative terminal 22 of supply 12. Since constantcurrent generators have an infinite impedance with respect to their loadimpedance, when control circuit 11 is functioning in thelimiting-regulating mode of operation, load current 16 will be limitedto the current output of constant current generator 17 independently ofvariations in supply 12 and the impedance of load 13. Consequently, thecurrent control circuit 11 provides excellent constant current stabilityin the limiting-regulating mode of operation.

A preferred embodiment of a circuit embodying the principles of theinvention is shown in FIGURE 4. Constant current generator 17 is apentode circuit energized by supply 23. The pentode circuit comprises apentode vacuum tube 24, cathode resistor 26, screen grid voltage supply27, and a variable grid bias supply including a voltage supply 28 andpotentiometer 29.

A load current supply 31 is electrically connected in seriesrelationship with a load impedance 32 through a first and second seriesconnected and oppositely poled diodes 33 and 34 respectively. Thecathodes of diodes 33 and 34 are electrically connected to a commonjunction 36. The serially connected diodes 33 and 34 are electricallyinterposed load 32 and the negative terminal of supply 31. Diode 33functions as the current comparison element as noted hereinbefore anddiode 34 functions to provide a threshold voltage drop which is equaland opposite to that of diode 33. Hence, during the nonlimiting mode ofoperation, the threshold voltages cancel effectuating a zero impedancepath from supply 31 to load 32.

The anode 37 of tube 24 is electrically connected to the common junction36 of diodes 33 and 34. The positive terminal of supply 23 iselectrically connected to the negative terminal of supply 31. Thenegative terminal of supply 23 is electrically connected through thecathode resistor 26 to the cathode '38 of tube 24. The control gridelectrode 39 is electrically connected to the wiper arm 41 ofpotentiometer 29. In operation wiper arm 41 of potentiometer 29 isadjusted to provide a bias voltage to grid 39 of tube 24 which allows apredetermined current 42 to flow through tube 24. Current 42 is utilizedas the forward bias current for diode 33 and, as noted supra, when theload current 43 is equal to or greater than the biasing current 42, thediode will be in the off state and hence, the current control circuitwill be functioning in the limiting-regulating mode of operation.Additionally, as noted supra, when the load current 43 is less than thebiasing current 42, diode 33 will be in the on state and hence, thecurrent control circuit will be functioning in the non-limiting mode ofoperation.

In the limiting-regulating mode of operation, load cur- 43 is limited tothe current output of the constant current generator 17. Load current 43will flow from the positive terminal of supply 31 through load 32,through diode 34, through tube 24 from the anode 37 to the cathode 38,through cathode resistor 26 and through supply 23 to the negative sideof supply 31.

Circuit parameters for advantageous operation of the current controlcircuit of the present invention as illustrated heretofore are asfollows:

(1) Diodes 33 and 34 IN2484 (2) Power supply 23 volts 75 (3) Powersupply 27 do 75 (4) Vacuum tube 24 6CB5 (5) Cathode resistor 26 ohms (6)Power supply 28 volts 10 (7) Potentiometer 29 kilohms 0-10 (8) Forwardbiasing current ma 25-1 The current control circuit of the presentinvention constructed in accordance with the above-note parametersexhibited less than 5% variation in load current in the limitingregulating mode over the current limiting range of l to 25 milliarnps.

While the present invention has been hereinbefore described with respectto a single preferred embodiment, numerous modifications and variationsare possible within the scope of the invention. For example, in place ofthe single pentode tube 24, two parallel operated pentode tubes may beused. Such a configuration provides a greater stability with respect tothe control circuit constant current characteristics. Furthermore, inplace of the single diodes 33 and 34, a plurality of light diodesserially con nected can be used. This enables the diode current path towithstand higher inverse voltages. Hence, the description of the presentinvention in terms of a single preferred embodiment is not intended tolimit the invention except by the terms of the following claims.

What I claim is:

1. In a non-linear current control circuit for limiting and regulatingthe current delivered to a load impedance from a unidirectional sourceof power, the combination comprising,

(a) a diode serially interposed said load impedance and said source,said diode poled to oppose current flow between said source and saidload impedance,

and

(b) a constant current generator electrically connected in parallelrelationship with said diode, said current generator connected tointroduce a current flow directed toward the junction of said diode andsaid load, whereby said current, together with said source of power,controls, the biasing mode of said diode.

2. A current control circuit as recited in claim 1 further defined bysaid constant current generator being a pentode tube circuit adaptedwith a separate D.C. power supply wherein said pentode tube circuitgenerates a constant current independent of said source of power.

3. A current control circuit as recited in claim 1 furthere defined by asecond diode serially interposed said load impedance and parallelconnected diode and constant current generator, said second diode poleto allow current flow from said source to said load impedance.

4. In a current control circuit for limiting and regulate ing thecurrent delivered to a load impedance from a unidirectional source ofpower, the combination compris- (a) at least a first semiconductor diodeserially interposed said load impedance and said source, said diodepoled to oppose current flow between said source and said loadimpedance,

(b) at least a second semiconductor diode serially interposed said firstdiode and said load impedance, said diode poled to allow current flowfrom said source to said load impedance,

(c) a pentode vacuum tube, the anode of said tube electrically connectedto the cathode of said first diode, the cathode of said tube seriallyelectrically connected with a resistor and suitable tube D.C. powersource to the anode of said first diode,

(d) a screen grid DC. bias supply electrically connected to the screengrid of said tube to introduce a positive voltage thereto with respectto said cathode, and

(e) a variable DC. control grid bias supply electrically connected tothe control grid of said tube, said control grid bias supply adjusted togenerate a selected current flow through said pentode tube whereby saidgenerated current flows through said load, creating a voltagethereacross, which voltage, in conjunction with said source of power,controls the the biasing mode of said first diode.

References Cited UNITED STATES PATENTS ORIS L. RADER, Primary Examiner.

0 T. J. MADDEN, Assistant Examiner.

1. IN A NON-LINEAR CURRENT CONTROL CIRCUIT FOR LIMITING AND REGULATINGTHE CURRENT DELIVERED TO A LOAD IMPEDANCE FROM A UNDIRECTIONAL SOURCE OFPOWER, THE COMBINATION COMPRISING, (A) A DIODE SERIALLY INTERPOSED SAIDLOAD IMPEDANCE AND SAID SOURCE, SAID DIODE POLED TO OPPOSE CURRENT FLOWBETWEEN SAID SOURCE AND SAID LOAD IMPEDANCE, AND (B) A CONSTANTGENERATOR ELECTRICALLY CONNECTED IN PARALLEL RELATIONSHIP WITH SAIDDIODE, SAID CURRENT GENERATOR CONNECTED TO INTRODUCE A CURRENT FLOWDIRECTED TOWARD THE JUNCTION OF SAID DIODE AND SAID LOAD, WHEREBY SAIDCURRENT, TOGETHER WITH SAID SOURCE OF POWER, CONTROLS, THE BIASING MODEOF SAID DIODE.